FIELDBUS - apachepersonal.miun.se

Mittuniversitetet

FIELDBUS

Industriell datakommunikation

Luca Beltramelli Email: [email protected]

Mittuniversitetet

References

Books:

• Practical Industrial Data Communications

by Reynders, Deon

Mackay, Steve

Wright, Edwin

• Industrial Communication Systems

by Wilamowski,

Bogdan M. Irwin,

J. David

Industriell Datakommunikation - Fieldbus 2

Mittuniversitetet

Program

04/05/2018

• Seminar I:

• Introduction to Fieldbus and Industrial Automation

• Overview of fieldbus technologies (Part 1)

07/05/2018

• Seminar II:

• Overview of fieldbus technologies (Part 2)

• Real Time Ethernet

• WirelessHART

Industriell Datakommunikation 3

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Control System


CONTROL

ALGORITHMPLANT

SENSOR

ACTUATOR+

-

Control System

Feedback

Reference Set

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Networked Control System


Communication

NetworkSensor(s) Actuator(s)

Controller(s)

Mittuniversitetet 6Industriell Datakommunikation - Fieldbus

Fieldbuses are real-time networks for sensors and actuators.

Used for the communication among sensors, actuators and controllers

What is a Fieldbus?

Fieldbus

Data and Nodes

Management

Diagnostic and

Integration

Safety and Security

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Real Time

“A real-time system is one whose logical correctness is based on

both the correctness of the outputs and their timeliness”

Soft vs Hard Real Time


Failure to meet

deadline

Catastrophic Failure Performance degradation

HARD RT SOFT RT

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Office Network: TCP IP, Ethernet

Plant Network: Ethernet, ControlNet

Fieldbus: FF, PROFIBUS PA, LON

Simple fieldbus or

Sensor Bus:

CAN, DeviceNet, SDS, ASI-bus, Interbus-S

The Automation Pyramid

Industriell Datakommunikation - Fieldbus

Mittuniversitetet

Traditionally in industries the communication was completly analog

Moving to digital communication brings many benefits:

• Immunity to noise;

• Less cabling;

• Better Diagnostic;

Fieldbus replace the traditional

4 – 20 mA analog technology.

9

Fieldbuses: the beginning

[mA

]

20

4

Measurement Range



4-20 mA vs Fieldbus

4-20 mA Fieldbus

Information Analog Digital

Signal Integrity Low (EMI,

Attenuation, ...)

High

Communication

Layer

Phyisical Physical, Data Link,

Application

Diagnostic Minimal Extensive

Installation cost High Low

Cost per device Low High

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One of the key requirements for the adoption of fieldbus is

the distribuited intelligence.

To access the fieldbus sensors and actuators are required

to implement a communication stack.

Smart Sensors:

• Computetion capabilities;

• Communicate in a digital way;

• They use a communication standard (at least layers 1 and 2 of ISO/OSI);

11

Fieldbuses: field devices


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Fieldbus Evolution

From the first proprietary solutions (’80) to the actually used standard (’90)

1969

First PLC

(Modicon 084)

1979

MODBUS

CAN

HART

1991 … 1996

Profibus FMS/DP/PA

FOUNDATION fieldbus

Predecessors Proprietary solutionsInternational

Standards



Fieldbus Evolution

From the first proprietary solutions (’80) to the actually used standard (’90)

2007

Release of

WirelessHART

2009

Release of

ISA100.11a

2010

Introduction

of IO-Link

2001 … 2006

EtherCAT (2003)

Eth/IP (2001)

Profinet (2004)

SafetyNET (2006)

…

Industrial Ethernet Wireless Networks



Layer ISO/OSI Model

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data link

1 Physical

Layer ISO/OSI Model

7 Application

2 Data link + MAC

1 Physical

OSI Model Implementation Model

Fieldbus and the OSI Model



Fieldbus: the applications

FIELDBUS

Factory Automation

Automative

Home Automation

Process Automation

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FIELDBUS FOR AUTOMOTIVE

16

Safety

• Redundancy, Check codes, very low data error rate

Determinism

• Synchronized communications, TDMA

Wireless networks are considered unreliable and, up to now, are used for

entertainment and extravehicular communications

IEEE 802.11p for data exchange between high-speed vehicles (V2V) in

the licensed ITS band of 5.9 GHz (5.85-5.925 GHz).

Examples:

LIN – very simple protocol (e.g. window automation)

CAN – CAN version with TDMA (e.g. ABS)

FlexRay – New (BMW, Audi, Mercedes …), increases baud rate with

respect to CAN (up to 10Mbytes/s) and adopts a TDMA with dynamic

slots assignment.


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FIELDBUS FOR HOME AUTOMATION

17

The low-cost is mandatory, non-invasive and mobile sensors

could be the future (wireless fieldbuses)

Primary needs: low-cost, simple installation, auto-configuration

There are a lot of proprietary solutions:

• CAN – based solutions (different application layers)

• Some emerging Ethernet-based solutions (security and costs problems)

• EIB, EHS and Batibus converge into Konnex (KNX) (ISO/IEC 14543-

3,EN50090)

• European Standard (Siemens, ABB, Bticino, Vimar, etc.)

• Wired and wireless

• LONWorks

• Widespread in USA

• Supported by electronic devices (Neuron Chips produced by

Toshiba, Freescale, Cypress)


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FIELDBUS FOR PROCESS AUTOMATION

18

• Safety is mandatory (particularly in chemical, oil, industries,…)

• High availability (redundant system)

• Reduce wiring (long distances) - the bus also powers the devices

• Speed is not important

• Cycle time are in the order of several hundreds of ms

• Timestamp is important in case of fault (resolution ~ 100 ms)

There are only two big players:

• PROFIBUS PA

• FIELDBUS FOUNDATION (it has local loop control between devices)

They use the same physical layer (Manchester, powered, 31.25kbaud)

but they are totally different at the data layer.

Wireless can be used for non critical processes, as it reduce wiring and

allow a range extension by suitable network topologies (mesh)


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FIELDBUS FOR FACTORY AUTOMATION

19

The main goals are:

• Fast and low-cost

• High rejection to noise

• Safety (e.g.protection of human operator)

Speed can be very important

• Reduced communication times means more products, i.e.

higher gain…

• Motion control (motor drives) need isochronous

communication

More than 20 fieldbuses for Factory Automation

• PROFIBUS DP is the most diffused but holds only the 15%

of the market (RS485, max 12Mbit/s)

• DeviceNet, CANOpen, use CANbus (max 1Mbit/s) Factory

environment is hostile for wireless technology (metal,

walls,…)


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The Ideal Fieldbus: some characteristics

• Transfers a “big number” of small data;

• Supports real-time traffic (Upper bounded response times, ex. 1ms..1s);

• Operates in hazardous environments (high temperature, vibrations, etc.);

• Is robust and easy to install;

• Has high availability (e.g. redundant architectures);

• Has continuous supervision and diagnostic;

• Manages long distances (100m .. 4 km);

• Has good data transmission rate (e.g. 50 kbit/s … 5 Mbit/s);

• Supports clock synchronization (e.g. milliseconds up to microseconds);

• Manages non real-time traffic for maintenance and diagnosis.

20Industriell Datakommunikation - Fieldbus


Fieldbus: the topology

Fieldbus daisy chain topology Tree topology

• Flexibility of the hardware of the measurement system

• Cable reduction

• Every node can share information with other nodes

•Different delays from node to the measurement system•Less realiable


Fieldbus: distributed measurements

In Industry to ensure good control and monitoring actions, sensor nodes

should…

A. Be synchronized

• Synchronization protocols

• Delay

• Jitter

B. Be identified and localized

• Identifier for each sensor

• Localization of moving sensor

C. Be qualified

• Uncertainty measurement

• Status report


Fieldbus: Measurement and Control

Measurement

• Data require a time reference

(timestamp)

Loop Control

• Delay must be limited

(deterministic transmission)


Fieldbus: Networked Control System (NCS)

Process

Controller

Communication Network

Actuator Sensor

Close loops in Process Automation• Process (temperature, humidity,…Tcycle > 1s)

Close loops in Factory Automation• Motion (positioning, speed, torque… Tcycle < 1 ms)


Fieldbus: a complex scenario

Ethernet

WorldFIPProfibus-PA

Batibus

BacNETHart

FieldBusFoundation

ControlNet

CANOpen

Profibus-FMS

DeviceNet

Profibus-DP

Modbus

Sercos

ControlFIP

Seriplex

CAN

Profisafe

M-Bus

IEEE 802.11

FlexRay

Ethercat

EtherLinkPROFInet

ModBus-RTPS

AND MANY OTHERS

!!!


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HART

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HART (Highway Addressable Remote Transducer)

• Developed in 1980, from 1990 is an open communication technology for process automation.

• Enables the transmission of digital information superimposed on analog 4-20 mA communication.

• The 4-20 mA is used for transmitting the analog data from sensor in the field.

27

LayerISO/OSI Model

HART

7 Application HART Commands

6 - 3

2 Data link HART Protocol Rules

1 Physical Bell 202 (FSK modulation)


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“Analog” for sensing information, digital for diagnostics

28

FSK modulation

‘0’ – 2200 Hz

‘1’ – 1200 Hz

The average value of the Frequency Shift Keying (FSK) modulation is

zero, the analog communication is unaffected by it.



HART: Point to Point communication

HART: Multi-point communication


HART Telegram

Three classes of commands:

• Universal Commands

• Common Practice Commands;

• Device-Specific Commands.


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Reference

• Official Website

• Practical Industrial Data Communications - Ch. 18a


https://www.fieldcommgroup.org/

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MODBUSRTU and ASCII

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• Application layer (Layer 7) messaging protocol

• Developed by Modicon in 1980

• Mainly Used in SCADA system

• Master-slave protocol

• Communication is initiated by the Master (Client)

• Slaves (Server) communicate only to the Master

• One communication at the time (Unicast or Multicast)

• Peer-to-peer

• UART (RS232, RS485)

• 1 master, <248 slaves


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Communication based around a

Query-Response cycle

The function code in the query tells

the addressed slave device the

action to perform.

(ex. read Input Registers, Force

Single Coil, Read Coil Status )

Modbus message Frame


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• Two serial transmission mode (no coexistence):

• ASCII mode

• 1 byte -> 2 char (0-9, A-F)

• Error Check -> LRC

• Bits per Byte:

• RTU mode

• 1byte -> 8 bit (0 … 255)

• Error Check -> CRC

• Bits per Byte:


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Reference

• Modbus over serial line

• Modbus Specifications


• Practical Industrial Data Communications - Ch. 8a


http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf

http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf

http://www.modbus.org/

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CANbus

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Controller Area Network (CAN)

Developed in ’85 by Bosch for automotive

• Random access bus (32 users, 1Mbps @ 40m)

• CSMA/CA

• Multi-master bus

• Asynchronous Serial Bus

• 4 frames: DATA (data exchange), REMOTE (request to send

data), ERROR (error signaling), OVERLOAD (temporary

unavailable)


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The CAN standard includes:

• Physical layer

• Data-link layer

• Message types

• Arbitration rules for bus access

• Methods for fault detection and fault confinement


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Phy layer

• Maximum bitrate 1Mbps.

• The bitrate depend on the bus length.

• The bitrate is limited to sense the collision between distant nodes.

• Twisted pair cable, differential transmission



• Bit Coding: NRZ (does not ensure enough edges for synchronization)

• Bit Stuffing is Required

• “open-collector like”, that is “0” level wins

• Automatic bus release if collision occurs and retransmission

(CAN, …)

(Profibus, Ethernet …)

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Higher Layer Protocols

• CANOPEN

• DEVICENET

• CAN Kingdom

• …

The Arbitration Field contains

a 11-bit (CAN 2.0 A) or 29-bit

(CAN 2.0 B) identifier for the

data.

Data with higher priority have

the MSBs at ´0´ and win the

arbitration.


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Reference


• Industrial Communication Systems - Ch. 31


https://www.can-cia.org/can-knowledge/

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PROFIBUS

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PROFIBUS (Process Field Bus)

Three versions of the standard:

• Profibus FMS (1991)

• PLC-PLC, PLC-SCADA, PLC-Field device (complex, obsolete)

• Profibus DP (1994)

• Simpler than FMS, normally 1 master (PLC), several slaves (field devices)

• Market leader

• Profibus PA (1995)

• Different and more robust physical layer (IEC 61158-2)


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LayerISO/OSI Model

FMS DP PA

User FMS Devices ProfilesDP - Profiles PA - Profiles

DP - Acyclic PartDP - Cyclic Part

7 ApplicationFieldbus Message Specification

(FMS)6 - 3

2 Data link (Fieldbus Data Link (FDL)IEC Interface

1 Physical RS-485 Fiber OpticIEC 61158-2 (Manchester

Encoded Power Bus)


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Profibus: the actors

• DPM1 (Master Class 1):central controller which exchanges data

with the connected I/O devices (slaves).

• Determines the bitrate.

• Handles the Token;

• Several class1 masters are permitted, typical devices are

PLC, PC.

• DPM2 (Master Class 2): diagnostic and startup tool, typically a

configuration tool, can control one slave at a time.

• Slave: passive station which acknowledges messages or

answers per request


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• At least one master is mandatory.

• Profibus networks allow for multiple masters.

• In total 127 stations can be addressed


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The slave is in one of four possible states:

• Power_ON / Reset

• Wait for Parameters

• Wait for Configuration

• Data Exchange

Cyclic data exchange between a Class 1

master and a DP slave can only take place if

the DP slave is in the data-exchange state

(DXCHG).

Master-Slave Communication

DP Slave State Machine

The master with the token can make use of

communications to address any other station

(masters and slaves).


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Master-Master Communication

Using a DP-DP gateway:

• combination of two mono master

systems;

• simple data exchange between the

two masters up to 244 byte.

Via the master-slave combination:

• whenever one master has the token the

other PLC can be a slave to this

master.


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Profibus transmission media

RS-485 Twisted cable

Baudrate 9.6 kbit/s to 12 Mbit/s

Maximum 32 devices

Distance can be extended by means of repeaters

• 12 Mbit/s @ 100 m

• 187.5 kbit/s @ 1000 m

Fiber Optic Single and Multi Mode

Baudrate 9.6 kbit/s to 12 Mbit/s

Distance can be extended by means of repeater to 100 km

MBP-IS

Twisted cable

Fixed Baudrate of 31.25 kbit/s

Maximum distance 1900 m

Between 10 and 32 devices per segments

Power Supply directly from the bus


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Fieldbus Data Link

• 4 types of frames

• Identified by the value of the first byte (Start Delimiter)

SYN: 33 bits at 1

SD1 10h 01101000

SD2 68h 10100010

SD3 A2h 00010000

SD4 DCh 11011100

Hamming Distance equals to 4

Note: SD3 practically unused


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Message SD2 (data exchange)

SD2 Start Delimiter (68H)

LE Information length (from 4 to 249)

LEr Information length repeated (Hamming distance = 4)

DA Destination address

SA Source address

FC Frame Control

DATA UNIT Data field (max length 246)

FCS Frame Check Sequence

ED End Delimiter (16H)

L Information length (L = from 4 to 249)


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Message SD1 (data request or Ack)

Message SD4 (token transfer)

Message SC (short Ack)

SD4 Start Delimiter (DCH)


SA Source address

SC Short acknowledgment (E5H)

SD1 Start Delimiter (10H)


SA Source address

FC Frame Control

FCS Frame Check Sequence

ED End Delimiter (16H)

L Information length (L = 3)


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GSD file (General Station Description)

• each slave or master class 1 device on PROFIBUS needs to have a device description file, the characteristic of each PROFIBUS device is described in the GSD-File;

• the GSD-file contains all device specific parameters e.g.:

• Supported Baudrate

• Supported Message Length

• Number of input / output data

• Meaning of diagnostic messages

• Options for modular devices e.g. which are available

• text file (ASCII-format);

• each configuration tool relates to the GSD information.


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